First dive to hydrothermal vent uncovers new deep-sea creatures

Researchers have found seven new animal species living along the Southwest Indian Ridge, almost 3,000 metres beneath the surface of the Indian Ocean, in an area currently targeted for deep-sea mining.

Five of these newly discovered species had never before been detected at other hydrothermal vents. They include two sea snails (belonging to the genera Lepetodrilus and Phymorhynchus) and a yeti crab (genus Kiwa).

The other two species, both scale worms from the polychaete family Polynoidae, had previously been found at other undersea vents but were never formally identified.

One of these other vents, part of the East Scotia Ridge, lies in the Southern Ocean - over 6,000 kilometres from the Southwest Indian Ridge.

'This suggests that scale worms can disperse vast distances across the ocean floor,' explains Museum researcher Dr Adrian Glover, who with Dr Helena Wiklund worked on the analysis of the specimens. 'But exactly how they do this is still completely unknown.'

'With this region of the Southwest Indian Ridge being considered for deep-sea mineral mining, an understanding of how these species are connected across vent fields is vital for any future conservation decisions.'

The hydrothermal vent chimney Ruyi Jingu Bang, which lies in the Longqi vent field. Credit: University of Southampton.

Slow burner

Hydrothermal vents, sometimes called black smokers, are fissures in the sea floor that release extremely hot, mineral-rich water. They form in areas where seawater comes into contact with deep, hot rocks such as mid-ocean ridges.

This vent field, known as Longqi (meaning 'dragon's breath'), lies around 2,000 kilometres southeast of Madagascar.

It contains multiple active hydrothermal vents, as well as inactive structures that have moved away from the hot zone. These vents and structures are rich in minerals, some of which are of potential economic interest.

Longqi was the first vent field to be discovered along the Southwest Indian Ridge, and one of the first along an 'ultraslow-spreading ridge' to be explored.

The ecosystems at these slow-spreading ridges, where the sea floor is spreading at a rate of less than two centimetres a year, are of particular scientific interest for a number of reasons.

For example, hydrothermal vents along slow-spreading ridges are spaced further apart than those along faster-spreading ridges. They are also active for far longer. These factors may affect how species spread between vents and how they evolve.

This Peinaleopolynoe specimen, also a scale worm, was first discovered at Longqi

Ecologically sensitive

The team explored the Longqi vent field back in 2011.

Led by the University of Southampton, they used a remotely operated vehicle to film the vents and retrieve specimens for study.

Dr Wiklund and Dr Glover then carried out DNA analyses of the specimens to identify them, comparing them with known species.

Many of the specimens were previously known from the nearby Central Indian Ridge, about 2,300 kilometres away. In addition, some of the new species are genetically similar to species found along the Central Indian Ridge.

However, most of the new species are so far only known at Longqi.

'We can be certain that the new species we've found also live elsewhere in the southwest Indian Ocean, as they will have migrated here from other sites,' says Dr Jon Copley, of the University of Southampton, who led the research.

'But at the moment no one really knows where, or how well-connected their populations are with those at Longqi.'

'Our results highlight the need to explore other hydrothermal vents in the southwest Indian Ocean, before any impacts from mineral exploration activities and future deep-sea mining can be assessed.'

Until researchers establish whether the species composition at Longqi is typical of slow-spreading ridges, the team suggests that the vent field meets many of the UN's criteria for an 'ecologically or biologically sensitive area'.

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